The present application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 2000-297691 filed on Sep. 28, 2000, the entire content of which is incorporated herein by reference.
The present invention generally relates to a vehicle seat. More particularly, the present invention pertains to a seat reclining device for a vehicle seat that permits adjustment of the angle of inclination of the seat back relative to the seat cushion.
An example of a known seat reclining device for a vehicle is disclosed in Japanese Unexamined Patent Publication No. H(Heisei) 11-70028. This published patent application describes a seat reclining device having a lower arm which is connected with the seat cushion, an upper arm which is rotatably supported by the lower arm and connected with the seat back, and a locking mechanism which has a plurality of pawls and a cam. The lower arm supports each of the pawls. Each of the pawls has an external gear which engages an internal gear formed on the upper arm. The cam forces the pawls to slide so as to engage or disengage the external gear with the internal gear. Plural spiral springs are also arranged between the cam and the upper arm. The spiral springs urge the cam to rotate so as to engage the upper arm with the lower arm.
In the known device described above, the axis of rotation of the cam can be moved within a predetermined range so that the pushing forces applied on each of the pawls by the cam toward the internal gear come to be equal, even if each of the parts has some dimensional dispersion or variation. This movement of the rotation axis of the cam compensates for dimensional variations in the parts and maintains a certain lock engagement between the upper arm and the lower arm. However, when the cam rotates to disengage the pawls from the upper arm, the rotation center of the cam is moved from its dimensional center because the plural spiral springs can not apply an even force due to their force dispersion. This does not cause significant difficulties during engagement, but can sometime cause an undesirable or uncomfortable noise problem during disengagement because all of the pawls are not simultaneously disengaged from the internal gear by the cam. That is, when the some of the pawls become disengaged from the internal gear, others still remain engaged and generate undesirable noise during the operation.
A need thus exists for a seat reclining device that is not as susceptible to the drawback mentioned above.
It would thus be desirable to provide a seat reclining device that does not generate noise to the same extent as in the known seat reclining device described above.
According to one aspect of the invention, a seat reclining device for a vehicle includes a lower arm, an upper arm rotatably supported by the lower arm, and a locking mechanism for preventing the upper arm from rotating against the lower arm. The locking mechanism has a plurality of pawls, each of which engages with one of the lower arm or the upper arm. A cam rotates to slide the pawls, and a guide portion is formed on the lower or upper arm for guiding the cam to match the rotation center of the cam with the center of the lower and upper arm upon disengagement of the external gears from the internal gear.
According to another aspect of the invention, a seat reclining device for a vehicle includes a lower arm, an upper arm rotatably supported by the lower arm, an internal gear formed on one of the lower arm and the upper arm, a locking mechanism having a plurality of pawls each provided with an external gear to engage with or be disengaged from the internal gear, a cam rotatable to slidably move the pawls and including a plurality of first projecting portions and a plurality of second projecting portions. The first projecting portions each engaging one of the pawls during rotation of the cam in a first direction to engage the external gear of the pawls with the internal gear. A shaft engages the cam to transmit a rotation force to the cam to rotate the cam in a second direction opposite the first direction to permit disengagement of the external gear of the pawls from the internal gear. A guide portion is formed on one of the lower or upper arms and is engaged by one of second projecting portions during rotation of the cam in the second direction so that a rotation center of the cam coincides with a center of the lower and upper arms.
According to another aspect of the invention, a seat reclining device for a vehicle includes a lower arm, an upper arm rotatably supported by the lower arm, an internal gear formed on one of the lower arm and the upper arm, a locking mechanism having a plurality of pawls each provided with an external gear to engage with or be disengaged from the internal gear, and a cam rotatable to slidably move the pawls during rotation of the cam in a first direction to engage the external gear of the pawls with the internal gear. A shaft engages the cam to transmit a rotation force to the cam to cause the cam to rotate in a second direction opposite the first direction to permit disengagement of the external gear of the pawls with the internal gear. A plurality of guide portions is formed on one of the lower or upper arms, with each guide portion including a pair of spaced apart projections between which is slidably arranged one of the pawls. At least one of the projections of each pair of projections has a guide surface portion engaged by the cam during rotation of the cam in the second direction.